One of the most welcome and big news in AutoCAD 2010 is the parametric functionality. In AutoCAD 2010 it is mainly to be used in 2D but to some extent it can at least drive 3D geometry as can be seen in this sample I created by only adding a few constraints.
Below is an animated GIF file showing how the reciprocator works when dragging the magenta handle around.
A reciprocator is also called ellipsograph because it the handle is describing an ellipse. Notice how the linear motion of the two green guides convert the motion to a circular or ellipse motion or the other way around the ellipse rotary motion is converted to a reciprocating motion in two axis.
You will find that you cannot add constraints to vertical objects like Walls in AutoCAD Architecture 2010. Hopefully it will be possible in a future version or you need to use Revit 2010.